Carburetor for small internal combustion engine having automatic choke control

ABSTRACT

An automatic diaphragm-type control for the choke valve of a carburetor for small single cylinder engines by which the choke valve is continually and automatically adjusted solely by engine suction opposing a spring force, to provide the optimum air-fuel ratio for combustible mixture drawn into the engine, not only during starting but at all operating conditions.

United States Patent inventors Joseph V. Reichenbach Milwaukee;

James L. Bartlett, Mequon; Paul R. Nau, Wauwatosa; Robert G. Thompson, Milwaukee, all 01 Wis.

Apr. 16, 1969 Dec. 7, 1971 Briggs & Stratton Corporation Wauwatosa, Wis.

Appl. No. Filed Patented Assignee CARBURETOR FOR SMALL INTERNAL COMBUSTION ENGINE HAVING AUTOMATIC CHOKE CONTROL 3 Claims, 11 Drawing Figs.

U.S. Cl 261/64 C,

26l/DIG. 68 Int. Cl F02rn 1/14 Field of Search 261/64.4,

64.3, 64, DIG. 68

[56] 7 References Cited UNITED STATES PATENTS 1,632,279 6/1927 Eckles 261/644 X 1,684,550 9/1928 Mallory 261/64 X 1,969,358 8/1934 Coffelder 26l/64.4 X 2,336,810 12/1943 Smith 261/644 X 2,979,047 4/1961 Rapplean et al. 261/392 X 3,278,172 10/1966 Meininger 261/D1G. 68 3,484,220 12/1969 Jones 261/644 X OTHER REFERENCES Briggs & Stratt, Circular No. MP- 5,373-5,378, 261- 264, (pgs. 1- 8) Primary ExaminerTim R. Miles Attorney-Ira Milton Jones ABSTRACT: An automatic diaphragm-type control for the choke valve of a carburetor for small single cylinder engines by which the choke valve is continually and automatically ad, justed solely by engine suction opposing a spring force, to provide the optimum air-fuel ratio for combustible mixture drawn into the engine, not only during starting but at all operating conditions.

PATENTEU DEC 7 I97! SHEET 1 OF 6 D L 0 W N A M 0 M Z T m 0 T M I w 6 a l wl L1 6&0 & 3 3 m u h flu w mm CPU 1 u M w. w fi 5. Wm Z Q J 3 2/ b, 4 W m ffl a ma PATENTEDDEB Han 3625492 SHEET 3 [IF 6 Paul HIE/2w 206:2"! 6. Thon yuan PATENTED m 1 IHYI SHEEI 6 OF 6 OPTIMUM SPRING SPRING DIAPHRAGM DIAPHRAGM OPTIMUM OPTIMUM RATIO OF FoRcE ON FORCE 0N DIAMETER AREA RESTRICTIONRESTRICTION RESTRICTION DJAPHRAGMDIAPHRAGM IN INCHES SQINCHES DIAMETER AREA AREA TO CHOKE CHOKE m INCHES SQJNCHES DIAPHRAGM CLOSED OPEN AREA (INGRAMSXIN GRAMF) .875 .6013 .010 .OOOOTS .0008 16.? 2a

|.o6zs .5866 (DIRECT SUCTION LIFT) Loezs .8866 (PUMP LIFT) L400 L539 .020 .oocsm .0002 22.8 42.74

A A A 5 A A WWW Joseph Vim/whiz? flmmlfiarf/M PavIHA/Ez; 054 2"? 1? T770502? CARBURETOR FOR SMALL INTERNAL COMBUSTION ENGINE HAVING AUTOMATIC CHOKE CONTROL This invention relates broadly to carburetors for small single cylinder internal combustion engines of the type widely used to power lawn mowers, and refers particularly to a control for the choke valve of such carburetors.

As far as is known, there never has been a single cylinder engine with a choke valve control which continually and automatically adjusts the position of the choke valve solely by engine suction acting in opposition to a spring force, and in so doing so regulates the air-fuel ratio of the mixture drawn into the engine that the optimum mixture is provided not only during starting but also during all running conditions of the engine. This invention achieves that desideratum.

Stated in another way, this invention completely obviates the need for any manual adjustment of the choke valve. Thus, instead of having to manually close the choke valve before cranking the engine and then quickly reopen it when the engine starts, the only thing required of the operator in starting the engine is to pull the starter rope.

As in some prior choke controls such as that of the Rapplean et al. U.S. Pat. No. 2,979,049,the present invention employs an engine suction responsive diaphragm to move the choke valve towards its open position in opposition to the force of a spring which at all times urges the valve towards its closed position and holds it closed when the engine is not running. But since prior choke controls of this type-and, for that matter, all known automatic choke controls-were concerned only with effecting an enriched mixture to facilitate starting of the engine, they did not contribute to the maintenance of an optimum mixture for good performance under all operating conditions. On the contrary, they often made this impossible due to the incorporation in the control of a thermostatic governor which overrode the suction responsive actuator.

The Skay U.S. Pat. No. 2,854,225, is an example of such thermostatically governed choke controls. In it, a thermostat prevents movement of the choke valve towards closed position after the engine temperature reaches a predetermined plateau. The control of the Rapplean et al. U.S. Pat. No. 2,979,047, on the other hand, employs a thennostatic governor to preclude opening of the choke valve by engine suction until the engine temperature reaches a predetermined point.

No one heretofore had discovered that a choke valve responsive only to engine suction and a spring force acting in opposition thereto could take care of both ease of starting and correct mixture under all operating conditions of the engine, which is the objective of this invention.

Since the choke control of this invention at all times so me ters the influx of air as to assure the optimum mixture for all operating conditions of the engine, a sudden increase in load does not bring about objectionable power loss. Everyone who has operated a power lawn mower has no doubt encountered the exasperating experience of having the engine stall when the load thereon was suddenly increased, as it would be in entering upon an area of longer grass. With this invention, such sudden increases in load results in a rapid adjustment of the choke valve towards closed position to momentarily enrich the mixture and keep the engine running. In this respect, the choke control of this invention acts like an automatic acceleration pump.

Although these two objectives-ease of starting and the prevention of power loss -impose incompatible demands upon the choke control, by this invention that incompatibility has been reconciled, with the result that the choke valve continually seeks a position near a location within its full range of adjustment, at which it meters the influx of air to the quantum necessary for optimum engine performance.

The foregoing is the primary object of the invention; its secondary purpose is to provide simple and practical structure by which the main purpose of the invention can be implemented.

With these observations and objects in mind, the manner in which the invention achieves its purpose will be appreciated from the following description and the accompanying drawings. This disclosure is intended merely to exemplify the invention. The invention is not limited to the particular structure or method disclosed, and changes can be made therein which lie within the scope of the appended claims without departing from the invention.

The drawings illustrate several complete examples of the physical embodiment of the invention constructed according to the best modes so far devised for the practical application of the principles thereof, and in which:

FIG. 1 is a perspective view of a carburetor for small single cylinder engines, embodying the choke control of this invention in one form thereof;

FIG. 2 is a cross sectional view through FIG. 1 taken on several planes, and somewhat diagrammatic to better illustrate the essential structure;

FIG. 3 is a side view of a carburetor similar to that of FIG. 1, but with a modified form of choke control, parts of said view being broken away and in section;

FIG. 4 is a sectional view through FIG. 3 on the plane of the line 44;

FIG. 5 is a side view of a carburetor similar to that of FIGS. 3 and 4, but with still another modified embodiment of the choke control;

FIG. 6 is a top view of the carburetor shown in FIG. 5, with a part thereof in section substantially on the plane of the line 66 in FIG. 5;

FIG. 7 is a more or less diagrammatic view illustrating the adaptation of this invention to a carburetor-fuel tank assembly wherein a single membrance provides both a diaphragm for the fuel pump and a diaphragm for the suction motor which actuates the choke valve;

FIG. 8 is a view similar to FIG. 7 but showing a somewhat modified structural arrangement;

FIG. 9 is a detail cross sectional view through FIG. 8 on the plane of the line 9-9;

FIG. 10 is a graph upon which is shown the permissible dimensional relationship between the diaphragm area and the area of the restriction through which the suction chamber under the diaphragm is communicated with the induction passage, and also showing the required spring force and rate parameters; and

FIG. 11 is a table depicting the dimensions of the restriction, and the spring force and the spring rate parameters that have been found to be correct for different sized diaphragms.

Referring to the drawings in which like numerals designate like parts, it will be noted that in every one of the several embodiments of the invention illustrated, the carburetor identified generally by the numeral 10, is mounted upon the top wall 11 of a fuel tank 12, which in turn is solidly fixed to the engine, not shown, as in the Lechtenberg et al. U.S. Pat. No. 3,194,224. Also in every case the carburetor comprises a die-cast body 13 formed to provide a mixture or induction passage l4 which connects with an intake pipe 15 on the engine, and an air inlet passage 16. As is customary, the upwardly facing inlet end of the air passage is adapted to have an air cleaner of the type shown in the bechtenberg U.S. Pat. No. 2,999,562, mounted thereon.

Fuel enters the induction passage through a port or jet 17 located adjacent to a throttle valve 18 mounted in the induction passage. The fuel entering the induction passage through the port 17 is metered by the usual needle valve 19 and the throttle valve is arranged to be manually opened and closed, as for instance in the manner employed in the Brown U.S. Pat. No. 2,908,263. The throttle valve is also adjusted by the governor with which the engine is equipped, as in the Brown et al. U.S. Pat. No. 2,529,243, and as is well known, the governor-whether it be of the air vane type, as in U.S. Pat. No. 2,529,243, or any other type-is responsive to engine speed and will effect opening of the throttle as speed drops due to an increased load and vice versa.

In all of the carburetors illustrated, an engine suction-actuated diaphragm fuel pump 20 lifts fuel from the tank into a cup or reservoir (not shown, but which is located directly beneath the top wall of the fuel tank) and engine suction manifested at the port 17 draws fuel from the reservoir into the induction passage. The aforesaid Lechtenberg U.S. Pat. No. 3,118,433, may be resorted to for an illustration of this pump-lifted fuel supply arrangement.

It should be understood, though, that this invention is also useful with direct vacuum lift systems wherein engine suction draws the fuel into the induction passage directly from the fuel tank, as in the Brown et al. US. Pat. No. 2,529,244.

The quantum of air drawn into the mixture or induction passage is controlled by a choke valve 21, which is of the rockable plate type, and in each case is mounted in the inlet passage 16.

Heretofore, the choke valve generally has been manually controlled, either directly at the carburetor or from some remote point, as shown for instance in the Reichenbach U.S. pat. No. 3,305,223, which provides a rather sophisticated manual choke control. But, as noted hereinbefore, there have been attempts to control the choke valve automatically, but those prior efiortsnotably the Skay US. Pat. No. 2,854,225 and the Rapplean et al. US. Pat. No. 2,979,047-were incapable of continually and automatically adjusting the position of the choke valve solely in response to changes in engine suction, which is the purpose of this invention.

Each of the structurally different carburetors shown in the drawings has a fluid pressure responsive actuator indicated generally by the numeral 25, connected with the choke valve and responsive to changes in engine suction manifested in the induction passage of the carburetor. In every case, the fluid pressure responsive actuator is of the flexible diaphragm type, wherein a flexible diaphragm 26 fonns one wall of a suction chamber 27 which is closed except for restricted communication with the induction passage through duct means 28.

Motion transmitting linkage connects the choke valve with the center of the diaphragm so that flexure of the diaphragm moves the choke valve between defined open and closed positions. This linkage comprises a crank arm 29 on an exposed end of the choke valve shaft 30 and a link 31 connecting the crank arm with the center of the diaphragm. Suction manifested in the suction chamber 27 thus will move the choke valve towards its open position in the absence of an opposing force greater than that produced by the suction.

Such an opposing force is exerted upon the choke valve by a compression type coil spring 33 confined between the diaphragm and a spring seat 34.

To this point, the structure described is common to all embodiments of the invention, in function, but there are differences between them.

THE EMBODIMENT SHOWN IN FIGS. 1 AND 2 In the structure shown in FIGS. 1 and 2, the carburetor body has a laterally projecting enlargement 36 on its base and a boxlike compartment 37 alongside and integral with the wall of the upwardly extending inlet passage 16. The underside of the enlargement 36, which is coplanar with that of the base, is fonned with a downwardly opening circular cavity 38, the sidewall of which is stepped to provide a downwardly facing shoulder 39. The flexible diaphragm 26 is received in the cavity 38 and has its peripheral portion clamped between the shoulder 39 and the upwardly facing rim of a cap 40 which is nested in the cavity and secured in position by engagement with the adjacent portion of the fuel tank top wall. A gasket is preferably interposed between the underside of the carburetor body and the top wall of the tank and this gasket extends across the underside of the cap 40. Hence the chamber fon'ned by the interior of the cap 40 and the diaphragm is airtight; this chamber is the suction chamber 27 in the FIG. 1 and 2 embodiment of the invention.

The cap 40 also provides the seat 34 for the spring 33, and to provide sufficient space for the spring, the cap has a downwardly projecting pocket 41 in which the lower end portion of the spring is received.

The suction chamber 27, i.e. the interior of the cap 40, is communicated with the induction rim of through the previously mentioned duct 28 which in this case comprises connecting drilled and cored passages 42, 43, 44 and 45, suction chamber the carburetor body and drilled holes 46 and 47 in the cap 40. The hole 47 opens to the suction chamber 27 and the hole 42 opens to the actuating chamber of the pump 20, which in turn is connected with the induction passage.

The link 31 of the linkage by which the diaphragm is connected with the choke valve passes through a hole in the top wall of the cavity 38 and enters the compartment 37, which together with a removable cover 49 houses the linkage.

THE EMBODIMENT SHOWN IN FIGS. 3 AND 4 The essential difference between the carburetor shown in FIGS. 3 and 4 and that of FIGS. I and 2 resides in the location of the fluid pressure responsive actuator, specifically the diaphragm 26. In this case, the carburetor body has a circular cavity 50 substantially in line with its induction passage 14 and directly adjacent to the inlet passage 16. This cavity has open communication with the inlet passage so that the link 31' can connect the diaphragm directly with the choke valve, the latter connection at 51 being the only one requiring clearance. Hence there is very little chance for slack in the motion transmitting connection between the choke valve and the diaphragm.

The peripheral portion of the diaphragm is clamped against the mouth of the cavity 50 by the rim of a cap 52 that is secured to the carburetor by screws 53. The cap and the diaphragm thus together form the suction chamber 27, and the cap also provides the spring seat 34 as in the FIG. 1 and 2 structure.

As shown in FIG. 4, the duct 28 by which the suction chamber is communicated with the induction passage comprises a long drilled hole 54 extending from the face of the carburetor body against which the diaphragm is clamped to the suction chamber of the fuel pump, which in turn is communicated with the induction passage through a port 55. A short drilled hole 56 and a small drilled hole 57, both in the cap 52, complete the duct.

THE FIGURE 5 AND 6 EMBODIMENT The embodiment of the invention shown in FIGS. 5 and 6 has the advantage of requiring a minimum amount of structural change in the body of the carburetor heretofore in use and shown in the Lechtenberg et al. US. Pat. No. 3,194,224. This advantage stems from the fact that the fluid pressure responsive actuator 25 is structurally completely independent of the carburetor body. Instead of using part of the carburetor body for a wall thereof, the fluid pressure responsive actuator is a self-contained unit, mounted on the carburetor body by a bracket 60.

This self-contained unit comprises a cup-shaped member 61 across the mouth of which the diaphragm is secured by a clamping ring 62 secured in place by screws 63, two of which also pass through one arm of the mounting bracket 60. Another am] of the bracket is bolted to the top of the base of the carburetor by one of the screws 64 that hold the carburetor to the top of the fuel tank.

The bracket also has an arm 65 which extends up from the top of the carburetor base and embraces a boss 66 on the carburetor body in which the shaft 30 of the choke valve is joumalled. A very stable two point securement is thus provided for the bracket 60.

As in the structure shown in FIGS. 3 and 4, the connection between the diaphragm and the choke valve in this case also consists only of a link 31 attached to the diaphragm and connected, as at 66', with the crank arm 29 on the end of the choke valve shaft 80. Reference may be had to the aforesaid Lechtenberg US. Pat. No. 3,194,224, for a disclosure of the manner in which the choke valve is attached to its shaft, and for the purpose of the hole in the center of the valve which appears in FIG. 6.

The duct 28 communicating the suction chamber 27 with the induction passage is formed by a hose 67 which has one end fitted onto a nipple 68 projecting from the side of the cup 61 and its other end fitted over a tubular stem 69 that passes through the cover 70 of the fuel pump 20 and extends into the body of the carburetor where it communicates through a drilled hole 71 with the actuating chamber of the pump and hence with the induction passage. The nipple 68 has an axial bore 72 which opens into the suction chamber 27. The hollow stem 69 is actually a slightly longer roll pin than that previously used to properly locate the cover of the fuel pump.

The structural independence of the fluid responsive actuator which this embodiment of the invention possesses, gives it a versatility which the other structures do not have.

THE FIGURES 7 AND 8 EMBODIMENTS OF THE INVENTION The embodiment of the invention shown in FIGS. 7 and 8 is characterized by the fact that a single membrane 74 provides the diaphragm 75 of the fuel pump and also the diaphragm 76 of the choke control and also by the provision of means for preventing the accumulation of fuel in the suction chamber 27 under the diaphragm 76. In this case, the top wall 77 of the fuel tank is formed to provide the pumping chamber 78 of the fuel pump and the suction chamber 27 of the fluid pressure responsive actuator by which the choke valve is adjusted.

The body of the carburetor, identified by the numeral 80, is formed to provide an actuating chamber 81 for the pump and a downwardly opening cavity 79 that registers with the suction chamber 27 of the choke control. It is also provided with duct means 28 by which the chamber 27' is communicated with the induction passage of the carburetor through the actuating chamber 81 of the fuel pump.

Wherever the suction chamber is below the level of the zone at which the duct 28 opens through the lower wall of the induction passage, it is necessary that means he provided to preclude entry of fuel which accumulates on the bottom wall of the induction passage from entering the suction chamber 27 In both FIGS. 7 and 8, one end of the duct 28 opens to the induction passage through its bottom wall, via a hole 82 (42 in FIG. 2), at a zone which is above the level of the suction chamber with which the other end of the duct communicates.

According to this invention, a portion of the duct 28 remote from said zone of the induction passage is disposed at a level higher than said zone to prevent fuel from flowing into the suction chamber of the fluid pressure responsive actuator.

In FIG. 7, this is achieved by forming a pocket 83 in the ceiling of the pump actuating chamber 81, and a drilled hole 84 which leads from the upper end of the pocket at a downward inclination to a recess 85 in the underside of the carburetor body. From this recess the duct is continued through a hole in the membrane 74 which opens to a hole 86 drilled into the adjacent portion of the fuel tank top wall, and a drilled hole 87 which connects the hole 86 with the suction chamber 27'.

In FIG. 8, the duct 28 consists of a drilled hole 90 which leads from the ceiling of the actuating chamber of the fuel pump at an upwardly sloping angle to the upper end of a hole 91 drilled vertically up into the carburetor body. The hole 91 connects with a recess 92 in the top of the tank through a hole in the membrane 74, and the recess 92 is communicated with the suction chamber 27' through a V-shaped groove 93 coined in the top face of the fuel tank.

It will be noted that in each of the structures referred to, the duct 28 includes an upwardly sloping passageway, so as to dispose a portion thereof at an elevation higher than that of the point at which the duct connects with the induction hole 84 with the pocket 83, and in FIG. 8 it is the junction of the drilled holes 98 and 91. In effect, therefore, the duct 28 in each case has an air trap to preclude flow of fuel that accumulates on the bottom wall of the induction passage into the suction chamber beneath the choke valve actuating diaphragm 76. Accumulation of fuel in this chamber would be detrimental to proper operation of the choke control.

The structure shown in FIG. 8 has another desirable feature which still further guards against the passage of fuel to the suction chamber beneath the choke valve actuating diaphragm. Any fuel which enters the pump actuating chamber 81 will be drawn therefrom by suction in the induction passage, through a hole 94 in the bottom of a bearing boss 95 in which the lower end of the throttle valve shaft 96 is journalled. The clearance between this shaft and its bearing is sufficient to allow suction in the induction passage to be manifested at the bottom end of the hole 94, which is close to the diaphragm and hence near the bottom of the pump actuating chamber 81.

In all of the structural embodiments of the invention illustrated and described, there are certain parametric relationships that must be maintained, and which have been found to be fairly critical. One of these relationships concerns the ratio between the diaphragm area and the capacity of the duct 28 whichcommunicates the induction passage with the suction chamber beneath the diaphragm. A restriction must be incorporated in this duct to dampen the effect of the pulsating engine suction upon the diaphragm, for otherwise the choke valve would flutter severely. In the structure illustrated in FIGS. 1 and 2, this restriction is formed by having part of the drilled hole 47 considerably reduced in diameter; in FIGS. 3 and 4, the drilled hole 57 is similarly reduced in diameter for part of its length; in FIGS. 5 and 6 it is the bore 72 which has a part thereof reduced in diameter; in FIG. 7, the reduction is in the drilled hole 86; and in FIG. 8 the coined groove 93, though of uniform cross section throughout its length, is small enough to provide the restriction. In every case the result is a restricting orifice of predetermined size in the duct 28.

However, the effectiveness of the restriction in the duct 28 must be properly related to the area of the diaphragm. THis entails establishing a particular ratio between the restriction in terms of its cross-sectional area, and the area of the diaphragm. This ratio should be such that maximum stability is assured for the choke valve in any position to which is adjusted, without sacrificing prompt response of the diaphragm to changes in engine suction, so that at all times the choke valve will seek a position at which the air-fuel ratio is best for good engine performance. This consideration resolves itself into a matter of determining the size of the reduced portion of the drilled hole 47 in FIGS. 1 and 2, the reduced portion of the hole 57 in FIGS. 3 and 4, the reduced portion of the hole 72 in FIGS. 5 and 6, the reduced portion of the hole 87 in FIG. 7, and the size of the V-groove 93 in FIG. 8.

Another relationship that must be taken into account is the ratio of the spring force and spring rate to the suctionproduced force which of course depends upon the area of the diaphragm.

Practical considerations such as avaialble space and cost determine the size, i.e. the area, of the choke valve actuating diaphragm. On a single cylinder 3%: hp engine with a 9-cubicinch displacement, a engine which is representative of the field with which this invention is primarily concerned, the diaphragm area is restricted to less than 1.50 square inches. But whatever diaphragm size is selected, its area becomes the constant to which the size of the restricting and the spring force and rate parameters must be related if the purposes of this invention are to be achieved. THese relationships are identified for several specific diaphragm sizes by the table, FIG. ll, of the drawings; and for other diaphragm sizes, the related parameters and ranges within which they should fall can be determined by reference to the graph, FIG. 10.

As stated above, the area of the restriction is used as a measure of the effectiveness of the restriction, but this is with the passage. In FIG. 7, this high point is the junction of the drilled 75 understanding that the length of the reduced portions of the drilled holes 47, 57, 72 and 87 is on the order of one thirtysecond of an inch, and that the V-notch or groove 93 has a length on the order of one-eighth of an inch. Obviously, any substantial increase in length of the restriction will increase its resistance to air flow, even to the point of seriously affecting the operation of the control. The length dimensions stated are both practicable and desirable. in the drawings, the size of the restriction formed by the reduced portions of the holes and/or a V-groove are exaggerated for clarity.

For a practical adaptation of the foregoing explanation, assume that the selected diaphragm area for a given engineagain, a 3% hp. single cylinder engine with a nine cubic inch displacement-is 0.886 square inches. The table (FIG. 11) identifies the optimum values of the different variables for the selected diaphragm size. In the second column of the table, the selected diaphragm area appears twice, once for a direct lift-type carburetor in which engine suction draws the fuel directly from the fuel tank, as in the Brown et al. US. Pat. No. 2,529,244; and again for a pump-lift-type carburetor like those illustrated in the drawings. In the third and fourth columns, the dimensions of the restriction, diameter and area are given, and if the carburetor is of the pump-lift-type, these dimensions are respectively, 0.019 and 0.000282.

The numerical values of the area of the restriction and of the diaphragm are used to arrive at the ratio which is given in the fifth column, and which is simply the quotient derived by dividing the restriction area by the diaphragm area. For the selected diaphragm area and pump type this ratio is 0.00032.

1n the sixth and seventh columns of the table, the spring force in grams per square inch of diaphragm area are given, respectively for the choke closed and choke open conditions. For the selected diaphragm area and carburetor type, these values are 15.75 and 21.70, respectively.

Reference to the graph (FIG. will show that the values chosen in the foregoing example all lie within the shaded area which delineates the range within which the variable parameters, i.e. restriction area, spring force and spring rate, must lie for any selected diaphragm area, if optimum results are to be obtained.

OPERATION With the engine not running, the spring force on the choke actuating diaphragm holds the choke valve closed. To start the engine, the throttle is manually opened in the customary manner, and the starter rope is pulled. THis cranks or turns over the engine at a speed of between 300 and 1,000 rpm. Since the choke is closed, the initial manifestation of suction in the carburetor caused by the first descent of the piston results in a rich mixture being drawn into the engine, since the only air available at this instant is that which occupies the induction passage and intake pipe or manifold. But immediately thereafter, perhaps still during the first descent of the piston and certainly during its second or third descentthe choke valve will be opened by engine suction, far enough to preclude flooding and, instead, bring about an optimum air-fuel mixture for a quick start.

Successive engine pulsations will cause the choke valve to flutter to some extent, but because of the dampening effect of the restriction, any fluttering which does take place is not serious and will not interfere with smooth engine performance.

As the load on the running engine varies, and the magnitude of the suction force on the diaphragm changes, the choke valve promptly seeks new positions between fully open and fully closed, to so meter the influx of air that the air-fuel ratio is corrected to meet the changed load conditions and keep the engine running smoothly.

THe prompt response of the control to changes in engine suction is especially valuable in preventing power loss due to a suddenly encountered increase in load. When that occurs, the opening of the throttle by the engine governor in an effort to meet the new load condition, diminishes the force of suction on the diaphragm and permits the spring force to move the choke valve far enough toward closed position to momentarily enrich the mixture and keep the engine from stalling. Under such suddenly encountered increased load conditions, the control performs as an accelerator pump.

An advantage of this invention not heretofore mentioned is that it requires no check valve, as in the Rapplean U.S. Pat. No. 2,979,047, which can be disabled by dirt in the fuel.

What is claimed as our invention is:

1. In a carburetor for single cylinder internal combustion engines having an induction passage in which engine suction is manifested, and a choke valve movable between defined closed and open positions to meter the admission of air into the carburetor and thereby govern the air-fuel ratio of the combustible mixture drawn into the engine through the induction passage,

means for automatically adjusting the position of the choke valve to provide optimum fuel mixture during cranking of the engine and at all operating conditions of the engine, said choke-adjusting means being of the type wherein l. a flexible diaphragm is connected with the choke valve through motion-transmitting means, so that flexure of the diaphragm imparts opening and closing movement to the choke valve,

2. the diaphragm forms the movable wall of a suction chamber communicated with the induction passage by duct means, flexure of the diaphragm in response to engine suction manifested in the suction chamber moves the choke valve towards its defined open position, and

3. a spring acting upon the diaphragm yieldingly urges the same in the opposite direction to move the choke valve towards its defined closed position,

said choke-adjusting means being characterized by:

A. the suction chamber being at all times communicated with the induction passage through said duct means;

B. an unvalved restriction of permanently fixed area in the duct means to dampen the pulsating effect of engine suction upon the diaphragm;

C. flexure of the diaphragm being at all times effected solely by the opposing spring an suction forces, so that any change in engine suction immediately effects an adjustment of the ratio of the air-fuel mixture; and

said choke control being further characterized in that D. the quotient obtained by dividing the area of the restriction by the area of the diaphragm lies between 0.001 and 0.0001; and

E. the strength of the spring and its rate are such that the force exerted by the spring when the choke valve is closed is between 12 and 24 grams per square inch of diaphragm area and between 18 and 45 grams per square inch of diaphragm area when the choke valve is open.

2. The carburetor of claim 1, wherein 1. the carburetor has a body with certain walls thereof defining a horizontally oriented induction passage so that liquid fuel that condenses in the induction passage can accumulate on the bottom thereof,

2. the suction chamber of the fluid pressure responsive means is a cup-shaped member located at the underside of the carburetor body with its bottom below the level of the induction passage,

. the diaphragm is clamped between the carburetor body and the rim of the cup-shaped member,

4. the duct means has one end thereof opening to the induction passage at a zone adjacent to the bottom thereof and its other end opening into the cup-shaped member, and

5. a portion of the duct means spaced from said zone is at an elevation substantially above that of said zone to preclude drainage of fuel from the induction passage into the suction chamber.

3. The carburetor of claim 1, wherein the carburetor has a body with a bottom wall, and further characterized in that the a cap telescoped in to the stepped mouth of the cavity with the peripheral portion of the diaphragm confined between said shoulder and the cap, and wherein the cap has a bottom surface flush with that of the underside of the carburetor body, so that upon securement of the carburetor to a fuel tank the cap and diaphragm are held in place.

i i =0 i UNITED PATENT OFFICE CERTIFICATE OF CORRECTION Patent Dated Inventor) Joseph V. Reichenbach at s].

It is certified that error appears in the above-identified patent and that said Letters Patentare hereby corrected as shown below:

Column 1 line 23, "2,979,049" should read 2 ,979,047

Column 4 line 6 "rim of" should seed --passsge-- Column 4 line 8 "suction chamber" should read --in-- Column 6 line 44 Insert "it" after --wh1ch-- Column 6 line 66 "restricting" should he --restriction-- Signed and sealed this 6th day of June 1972.

(SEAL) Attest:

EDWARD M.FLETCI ER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents FORM Po-mso (10-69) USCOMWDC and; 9 U S, GDVCIIMIENI' 'IINYING OFFICE li! li-III 

1. In a carburetor for single cylinder internal combustion engines having an induction passage in which engine suction is manifested, and a choke valve movable between defined closed and open positions to meter the admission of air into the carburetor and thereby govern the air-fuel ratio of the combustible mixture drawn into the engine through the induction passage, means for automatically adjusting the position of the choke valve to provide optimum fuel mixture during cranking of the engine and at all operating conditions of the engine, said choke-adjusting means being of the type wherein
 1. a flexible diaphragm is connected with the choke valve through motion-transmitting means, so that flexure of the diaphragm imparts opening and closing movement to the choke valve,
 2. the diaphragm forms the movable wall of a suction chamber communicated with the induction passage by duct means, flexure of the diaphragm in response to engine suction manifested in the suction chamber moves the choke valve towards its defined open position, and
 3. a spring acting upon the diaphragm yieldingly urges the same in the opposite direction to move the choke valve towards its defined closed position, said choke-adjusting means being characterized by: A. the suction chamber being at all times communicated with the induction passage through said duct means; B. an unvalved restriction of permanently fixed area in the duct means to dampen the pulsating effect of engine suction upon the diaphragm; C. flexure of the diaphragm being at all times effected solely by the opposing spring and suction forces, so that any change in engine suction immediately effects an adjustment of the ratio of the air-fuel mixture; and said choke control being further characterized in that D. the quotient obtained by dividing the area of the restriction by the area of the diaphragm lies between 0.001 and 0.0001; and E. the strength of the spring and its rate are such that the force exerted by the spring when the choke valve is closed is between 12 and 24 grams per square inch of diaphragm area and between 18 and 45 grams per square inch of diaphragm area when the choke valve is open.
 2. The carburetor of claim 1, wherein
 2. the diaphragm forms the movable wall of a suction chamber communicated with the induction passage by duct means, flexure of the diaphragm in response to engine suction manifested in the suction chamber moves the choke valve towards its defined open position, and
 2. the suction chamber of the fluid pressure responsive means is a cup-shaped member located at the underside of the carburetor body with its bottom below the level of the induction passage,
 3. the diaphragm is clamped between the carburetor body and the rim of the cup-shaped member,
 3. a spring acting upon the diaphragm yieldingly urges the same in the opposite direction to move the choke valve towards its defined closed position, said choke-adjusting means being characterized by: A. the suction chamber being at all times communicated with the induction passage through said duct means; B. an unvalved restriction of permanently fixed area in the duct means to dampen the pulsating effect of engine suction upon the diaphragm; C. flexure of the diaphragm being at all times effected solely by the opposing spring and suction forces, so that any change in engine suction immediately effects an adjustment of the ratio of the air-fuel mixture; and said choke control being further characterized in that D. the quotient obtained by dividing the area of the restriction by the area of the diaphragm lies between 0.001 and 0.0001; and E. the strength of the spring and its rate are such that the force exerted by the spring when the choke valve is closed is between 12 and 24 grams per square inch of diaphragm area and between 18 and 45 grams per square inch of diaphragm area when the choke valve is open.
 3. The carburetor of claim 1, wherein the carburetor has a body with a bottom wall, and further characterized in that the suction chamber of the fluid pressure responsive means is provided by a cavity in the bottom wall of the carburetor body, wherein the underside of said bottom wall is flat and adapted to seat upon the top wall of a fuel tank, wherein the mouth of said cavity is stepped to provide a shoulder spaced upwardly of the underside of the bottom wall, the carburetor being further characterized by a cap telescoped in to the stepped mouth of the cavity with the peripheral portion of the diaphragm confined between said shoulder and the cap, and wherein the cap has a bottom surface flush with that of the underside of the carburetor body, so that upon securement of the carburetor to a fuel tank the cap and diaphragm are held in place.
 4. the duct means has one end thereof opening to the induction passage at a zone adjacent to the bottom thereof and its other end opening into the cup-shaped member, and
 5. a portion of the duct means spaced from said zone is at an elevation substantially above that of said zone to preclude drainage of fuel from the induction passage into the suction chamber. 